water on floor

I notive every once in a while there is a small puddle on my cellar floor by my furnance, and it smells a little like antifreeze. Is this normal that the furnance would let go of some water once in awhile...it seems to be coming from the back..but, by the time I notice it, the part by the furnance is dried. Thanks

If it's NOT a high efficiency system and you have exhaust condensation occuring something's wrong and it needs to be corrected before damage is done. Oil exhuast condensate is particularly corrosive and more critical to fix quickly, but don't let NG/propane condensation go for months either or you'll be replacing flue liners &/or heat exchangers or more.

If this is a boiler (and not a hot-air furnace), there are other ways water could end up on the floor.

I may not use the right terminology, it's run with oil, and uses hot water to circulate the heat thru registrars, it's a Weil Mclain, tankless coil heater,(boiler, furnance)...does this help determine the cause??? It only happens once in awhile. We have had a lot of heavy rain for the past weeks,..I do have a cap on top of my chimney.
any suggestions
Thanks
Barry

I may not use the right terminology, it's run with oil, and uses hot water to circulate the heat thru registrars, it's a Weil Mclain, tankless coil heater,(boiler, furnance)...does this help determine the cause??? It only happens once in awhile. We have had a lot of heavy rain for the past weeks,..I do have a cap on top of my chimney.
any suggestions
Thanks
Barry

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If it's pumped hot-water circulating through convectors/baseboards/radiators etc it's a "hydronic boiler", not a furnace.

With a vent cap keep the weather out it's not likely to be rain- it could be leaking, which could be good or bad, depending...

Somewhere on the thing (often under a removable panel) there should be pressure & temperature gauges. Somewhere on the plumbing there should also be a valve for filling the system with water, and (most often) an automatic filler to feed fresh water into the system to make up for any leaks. Under normal conditions the pressure will be between 12-20psi (doesn't need to be any more than 12 in most installations) and the automatic filler valve will keep it there until/unless it's leaking great gushers somewhere.

As a diagnostic, take note of the pressure, then turn off the valve isolating it from the domestic water. If it's leaking, over several hours to several days the pressure will slowly fall (don't let it go under 8psi though.) If that's the case, get a professional assessment as to whether it's repair vs. replacement time. (I'm gonna guess this beast is over 25 years old, and that it's replacement-time if it's leaking, no matter what.) If it's been leaking a long time letting fresh water into the system, the system will be corroding and rusting from the inside, making it even more leak prone (and lower efficiency heat exchange at the internal plates.)

If it holds steady, the drips could be condensate, which is potentially damaging. This could be aggravated by summer time short-cycles at lower temp since it's providing only hot water, not heat, so the flues may not get to full temp allowing the exhaust to condense and drip down the flue into the boiler before finding it's way to the floor. Over time (sometimes not very MUCH time) this will rust & erode the heat exchanger, which will lose efficiency then fail (in a more majorly leak fashion.) If it happens in the same place every time, put a saucer down there and capture some. Oil condensate smells a bit like automotive battery acid, but won't be as strong.

After testing for dropping pressure over then next week or so, be sure to turn the filler valve back on. Odds are low (but non-zero) that it would leak enough to cause a steam explosion- you'll usually start to get a lot of sizzle/rattle/pop out of the heat exchangers when the burner is firing with the system at low pressure and notice it long before it runs dangerously dry. But running it at low pressure isn't good for it long term. At low pressure oxygen gets in through the various seals which can prematurely destroy cast iron circulation pumps, erode the heat exchanger plates, etc.

Be prepared to test your captured drip by getting a pH test kit- if the pH of the drip is 3 or less, it's condensate. If it's over 4, it's more likely to be something else like boiler leak water. There should be a valve on the near-boiler plumbing for flushing/purging the system where you can draw yourself a sample to compare to the drip too. Highly discolored is normal, but shouldn't look/feel like mud either. In a small glass, hazy & translucent is OK. If it's opaque with heavy sludge forming on the bottom after sitting for day, filtering (or more) is probably in order.

No matter what you find, getting an assessment from a pro won't hurt and shouldn't cost TOO much if you combine it with a burner tune-up. If the thing has never been cleaned or tuned up odds are its running well below 60% efficiency and it's probably capable of ~75% or better, no matter how old it is. If it's a real antique, it may be time to bite the bullet and go with a higher-efficiency unit with an indirect-fired HW tank. The efficiency of tankless hot-water coils on high-mass boilers is OK during the peak of the heating season, but sucks during the rest of the year- it's probably costing you 50-100 gallons/year on just the hot water heating end compared to what you'd get with a medium-mass 85% AFUE boiler with an indirect-fired hot water tank. (And the difference even more than that on space heating, if it's an oversized rarely-tuned antique.)

If it's looking like boiler replacement time, this may be a bit of a slog to read in full, but at least pore over the tables & graphs on this test report:

Note in Table 3 that the efficiency all boilers fall off when they're 2-3x oversized (meaning they put out 2-3x the heat per hour than you need to stay warm on the coldest hours of the coldest night of the year.) Yours is probably closer to system 1 or system 10, and likely to be 3x oversized or more if you've had any insulation upgrades in the history of the house (unless you got lucky and the heating contractor did a full heat loss analysis when the boiler was installed, in which case it's only 2x oversized.)

You may be able to analyze the sizing of the existing unit yourself if you have good oil use records over a heating-season or two and want to look up the heating-degree-day data. (This is usually more accurate than the various calculation methods based on wall/roof/window/door area, like ACCA Manual-J or similar.) There's a pretty-good heat load analyzer tool based on the Brookhaven Nat'l Labs test data from that other document downloadable here:

Read the documentation that comes with it- if you know the heating degree-days you can enter a "K-factor" and get closer to the true heat load, but lthe gallons/year combined with the location is still pretty good. Then read the heating output btu/hour off the nameplate for the rest, and it'll calculate the true heat load for you. If the nameplate output is 3x or more the number it came up with for a heat load (and it often is), it's probably time to scrap it and start over with something no more than 1.3x the actual heat load. Just getting something "right sized" (at the same steady-state thermal efficiency) will typically cut your fuel use by a third or more, whereas just tuning up old beast to optimum efficiency (for a lot less money, of course) is usually good for ~10%.

Where the cost/benefits break down vary a lot with the house/system particulars (and the price of heating oil, of course.) I don't expect to see oil hit last year's peak any time soon, but neither do I anticipate this years' low to survive the heating season. World demand for motor fuel is likely to push prices dramatically over the next decade. If there's a gas main on your street it may be worth switching fuels when swapping boilers. Natural gas prices aren't strongly linked to motor fuel prices, and the domestic supply in the US is large. Coal-seam gas production from exploration done over the past decade or so is coming online at an increasing pace, driving the price ever lower. While oil has traditionally been somewhat cheaper than gas for heating, it's doubtful that it will continue to be so over the next coupla whiles.